1. Field of the Invention
This invention relates to copper-base alloys. In one aspect, the invention relates to a method of removing surface oxides from a copper-base alloy while in another aspect, the invention relates to removing complex thermal oxides, particularly aluminum oxides, from the surface of aluminumcontaining copper-base alloys.
2. Description of the Prior Art
The art contains various references teaching different methods for removing surface oxides from copper-base alloys. Representative of these teachings are Toth, U.S. Pat. Nos. 2,726,970; Grof, 3,274,114; and Ford et al., 3,646,946.
Toth teaches a multi-step process comprising cleansing the copper-base alloy in an alkaline solution, rinsing the alloy in cold water followed by contacting the alloy with a solution of strong sulfuric and nitric acid, and then twice rinsing the alloy in cold running water. The alloy is finally immersed in a solution containing a thio compound, e.g. sodium thiosulfate, and oxyboron compound, e.g. sodium tetraborate, and a sulphonate, e.g. an alkyl aryl sulphonate.
Grof teaches the use of a composition that has both tarnish removing and tarnish inhibiting properties and which is particularly useful in connection with copper or copper-containing alloys. The composition consists essentially of 5-40 percent by weight of sulfamic acid, 5-40 percent by weight of either a hexavalent chromium salt or an anhydride of a hexavalent chromium compound, and water.
Ford et al. teach a process for removing surface oxides from copper alloys which consists of a duplex treatment requiring a first immersion in a hot alkaline solution followed by a second immersion in a hot mineral acid solution. The pH of the alkaline solution is between 10 and 14, preferably between 11 and 14 and is typically a solution of sodium hydroxide. The mineral acid solution has an acid equivalent to a sulfuric acid solution of 3-50 percent by volume and is preferably sulfuric acid. This method is taught to be useful for cleaning copper-base alloys which have been annealled-to-temper.
While these and other copper-base alloy cleaning processes all demonstrate utility, none are completely satisfactory. These processes leave considerable amounts of copper oxide on the surface of the alloys and where the alloys contain aluminum and zinc, considerable amounts of aluminum and zinc oxide are also left on the alloy surface. In addition, not all of these processes are amenable to cleaning a copper-base alloy moving through a production line and of those (e.g. U.S. Pat. No. 3,646,946) that are, none are entirely satisfactory in terms of overall efficiency, e.g. energy consumption, residence time, reagent consumption, etc.